Preparation of rare metals by electrolytic decomposition of their fused double halogen compounds



Patented Jan. 19, 1932 FRANK H. BRIGGS, OF BLOOMFIELD, NEW JERSEY, ASSIGNOR TO WESTINGHOUSE LAMP GOMQPANY, A CORPORATION OF PENNSYLVANIA PREPARATION OF BABE METALS BY ELECTROLYTIC DECOMPOSITION OF THEIR FUSED DOUBLE HALOGEN COMPOUNDS No Drawing.

Application filed may 11,

, fused halogen bath containing an ionizable halogen compound of the rare refractory metal, recovering the metal powder from the fusion mixture by suitable lixivlation means, thereafter compacting and sintering the metal powder in an inert environment to a coherent ductile body.

Heretofore many methods have been devised for the preparation of the so-called rare refractory metals. Most of these methods have been directed to the production of the metal by reducing compounds of the same with highly reactive metals such as sodium, magnesium, aluminum and calcium. Due to the extreme activity of the rare refractory metals in the powder state, great difficulty has been encountered in preparing them substantially free from deleterious impurities of carbon, nitrogen, oxygen, etc. Such reduction methods as have heretofore been developed have been relatively expensive to operate.

Specifically, this invention is directed to the production of the rare refractory metal uranium by the electrolytic decomposition of its ionized fused halogen salts. Heretofore it has been considered that the high chemical activity of uranium would prevent the preparation of the met-a1 by such electrolytic methods, but I have developed a method whereby such electrolytic decomposition of uranium salts may be effected.

One of the objects of this invention is to provide a method of producing rare refractory metals by electrolytic decomposition of their fused halogen compounds.

Another object of this invention is to provide a method of preparing uranium by the electrolytic decomposition of fused uranium halogen compounds.

Another object of this invention is to provide a method whereby uranium metal may be prepared by electrolytic decompositionof 1928. Serial- NO. 277,098.

fused double halogen compounds of uranium with the alkali metals.

Another object is to provide a cheaper and moreeflicient method than heretofore available for the production of uranium metal powders.

Another object of this invention is to provide a means of recovering the uranium and other refractory metal powders from the fusedbath and to compact and sinter the same into coherent metal bodies which may subsequently be mechanically deformed into shapes useful inthe arts.

Other objects and advantages will become ap arent as the process is described.

11 the preparation of uranium by my process I preferably employ as an ionizable halogen compound of the metal an anhydrous double halogen compound of an alkaline metal with uranium and specifically I prefer to use the double fluoride compound of uramum with potassium, having a formula KUF This salt may be prepared as set forth 1n copending application Serial No. 168,826, entitled Preparation of an oxide-free halide of a rare refractory metal, and assigned to the same assignee as the present invention.

The reasons why I prefer to use this particular double alkaline uranium compound 1n the electrolytic preparation of uranium are as follows: In the first place, I have found that in order to prepare substantially pure uramum I must use substantially pure uramum compounds in the electrolytic process and that this method of crystallizing uranium double fluorides ensures absolute purity as regards the uranium salt.

Secondly, I have found that fluoride fusions of uranium are more stable than chlorides, bromides, or iodides in the open air and do not tend to break down and form oxygen compounds by reaction with atmospheric oxygen. A third factor influencing the selection of this compound has been that oxygen reacts with uranium to form highly stable compounds which are insoluble and undecomposable in the alkaline fluoride fusion, and which are thereafter extremely diflicult to remove from the metal powder which may be producedby the electrolysis procedure,

As a specific embodiment of my invention I prepare a fusion mixture comprised of a u I natlon of the two alkalme fluondes men-' proximately one part sodium fluoride and two puma potassium fluoride which fluorides should preferably also have fusion.

been purified and freed of contaminating'impurities likely to be reduced to metal form during the subsequent electrolysis procedure.

To this fusion mixture either prior 110 01 after fusion I add the double alkaline fii10r1de compound of uranium, in such an amount as will completely dissolve in the fusion mlxtux-e, which vvill afipproximately be b itWeen twentyve per ce nt by welght of of he fuslon mixture employedde bath,

the

liberated uranium being very dense (18.7) and heavy, falls to the bottom of the fused bath and is protected from reacting wlth the gases of the atmosphere by the fused fluoride From time to time frequent addltions of alkali fluorides or of double alkali uranium fluoride may be made to render the, process a continuous one.

The current applied would depend uponthe size of the bath, the spacing and the area of the electrodes, the rate at which it is deslred to deposit the metal, and other factors. In the practice of my invention I have found that a current density at the cathode of approximately .27 amperes per cm is nearly the correct current density. This may vary, h0w- I too high and I have found that .90 amperes per cm is approximately right to prevent the development of the so-called anode ef-' feet or polarizing at the anode which occurs when the amount of fluorine liberated is sufficient to coat or insulate the anode from the fused bath.

The materials employed in the construction a of a suitable electrolytic chamber to conduct the electrolysis may be of any material which will resist the corrosive action of the fluoride fusion, namely carbon, graphite, nickel and some of the cast corrosive resistant alloys such as nichrome, hardite, etc.

The electrodes may be of carbon, if desired,

' or of any material resistant to the corrosive action of the flux or fluorine gas liberated.

The temperature of the fused bath will vary with the amount of anode eflect developedand will range in the neighborhood of 700 C. to 800 C. While I have specified as. a fusion mixture an alkaline fluoride fusion comprised of one part sodium fluoride (NaF) to two parts potassium fluoride (KF), it is to be understood that such a fluoride fusion may vary withinwide limits and still fall within the scope of this invention.

I may use, for instance, any other co1i1bildo oompoumh, such as ammonium fluoride, to further thin the bath, or, I me add thereto a proportion of any of the a aline earth fluorides. For the reason,fhowever, that I must subsequently recover from the fusion the metal powder substantlally free from d.c1eterious impurities I prefer to emg1oy m the practice of my invention those uorldes which in. addition to fillfilling the other requirements of my process are capable of subsequently being removed by solution in f i the conclusion of the electrolysis the llberated metal powder may be eeeeee red from the fusion in the following manner- The fused bath. is allowed to cool to room temperature in the electrolytic chamber,

thereafter it may be removed and crushed (approximately 1 part acid to 4 parts water) to dissolve out acid soluble impurities. Such acid washes should preferably be made in the cold, following which the metal powder is put through any well known minerals separation procedure to remove accompanying insoluble impurities, such as carbon, oxides, etc. Thereafter the metal powder is washed free of water by an alcohol wash followed by an ether wash, after which it is thoroughly dried in vacuo.

I have found that frequently such metal powders of uranium, prepared by my process, arepyrophoric and will spontaneously ignite and burn when exposed to the atmosphere. I have found, however, that by suitable regulation of the current density at the cathode during deposition of the metal powder to substantially increase the crystalline size thereof, such pyrophoric tendencies are mltigated, and the metal powders may subsequently be compacted, sintered and con-.

solidated to coherent metal.

The method I may employ in the sintering and consolidation process is similar to that disclosed in copending application Seerial No. 684,908, Marden et a1, entitled Sintering and fusing uranium into a coherent body and which copending application is assigned to the same assignee as the present invention. I

The process in brief, contemplates sintering and fusing (if necessary) substantially pure metal powders by initially substantially effecting de asification of the same at temperatures be ow the sinteri'ng temperature of the metal powder by slowly heating the powders in a high vacuo, removing the lib erated adsorbed or absorbed gases as fast as they are liberated, and thereafter raising the temperature to the sintering (or fusing) temperature (if desired). In the copending application the heating has been specified as bein by inductive heating, but, of course, any other method of heating may be applied.

Having outlined in the broadest aspect the nature of my invention and specifically directed the same to the production of uranium,

it is apparent that there may be many variations of the same whereby essentially the same result may be obtained, but such variations are anticipated as may fall within the scope ofmy claims.

25, Other refractory metals ma be prepared in a similar manner through t e practice of my invention, such as tantalum, columbium, chromium, zirconium, thorium and the like, but those that may be so prepared are considered to fall within the scope of the term rare refractory metals.

What is claimed is: p 1., The process of preparing uranium comprising electrolytically decomposing a double halogen compound of uranium in solution in a fused bath comprised of alkali halogen compounds.

I 2. The process of preparing uranium comprisin electrolytically decomposing a double fluori e compound of uranium in solution in adfused bath comprised of alkali metal fluor- 1 es.

3. The process of preparing uranium comprising electrolytically decomposing the double potassium uranium fluoride (KUF in solution in a fused bath comprised of potassium and sodium'fiuorides.

4. The process of p eparin uranium comprised in electrolytlcally ecomposing a I fused bath composed of potassium fluoride (2 parts) sodium fluoride (lpart) potassium and uranium double fluoride up to 25 percent of the total (by wei ht).

In testimony whereoi I have hereunto subscribed my name this 9th day of May,

FRANK H. DRIGGS. 

